Continuous spike-waves during slow waves sleep: a clinical and electroencephalografic study in fifteen children

Ponta-onda contínua do sono lento: estudo clínico e eletrencefalográfico em quinze crianças

CONTINUOUS SPIKE-WAVES DURING SLOW WAVES SLEEP

A CLINICAL AND ELECTROENCEPHALOGRAFIC STUDY IN FIFTEEN CHILDREN

ADRIANA A. F. DJABRAIAN^*, MARCUS SABRY AZAR BATISTA^**, MÁRCIA M. DE LIMA^***, DÉLRIO FAÇANHA SILVA^***

ABSTRACT - We report on the clinical and EEG features of 15 patients with the syndrome of "continuous spike waves during slow wave sleep" (CSWSS). The differential diagnosis of CSWSS includes benign epilepsy of childhood with centro-temporal spikes, and Landau-Kleffner and Lennox-Gastaut syndromes. We found normal CT and MRI features in 6 cases, periventricular leukomalacia with and without diffuse brain atrophy in 4 cases and hydrocephalus in 1 case. There was no association between specific neurological findings and CSWSS. Nine of our cases had relatively focal discharges, like some cases from the literature. The occurrence of CSWSS appears to be age-related, generaly between the ages of 5 to 12 years, with a strong temporal relation to the neupsychological deterioration in its nature, severity and prognosis. We believe that this striking disorder has been overlooked and that routine sleep EEG studies on epileptic children may disclose additional cases of CSWSS.

KEY WORDS: electroencephalogram, sleep, epilepsy, continuous spike-wave.

Ponta-onda contínua do sono lento: estudo clínico e eletrencefalográfico em quinze crianças

RESUMO - Relatamos as características clínicas e eletroencefalográficas de 15 patientes com a síndrome de ponta-onda contínua do sono não-REM (POCSNR). O diagnóstico diferencial da POCSNR inclue a epilepsia benigna da infância com pontas centro-temporais e as síndromes de Landau-Kleffner e Lennox-Gastaut. Encontramos TC e RNM de crânio normais em 6 casos, leucomalácia periventricular em 4 e hidrocefalia em 1. Não houve associação de achados neurológicos específicos e a POCSNR. Nove dos nossos casos tinham descargas relativamente focais, como alguns casos da literatura. A ocorrência da POCSNR parece ser idade-dependente, geralmente entre 5 e 12 anos, com forte relação temporal à deteriorização neurocognitiva, em sua natureza, severidade e prognóstico. Acreditamos que esta síndrome tem sido pouco diagnosticada e que a realização rotineira de EEG em sono em crianças epilépticas possa revelar novos casos de POCSNR.

PALAVRAS-CHAVE: eletroencefalograma, sono, epilepsia, ponta-onda contínua.

The epilepsy with continuous spike-waves during slow wave sleep (ECSWSS) was first described by Patry et al. (1971) under the title "subclinical electrical status epilepticus" induced by sleep in children. Nowadays it is defined as "continuous spike waves during slow wave sleep"(CSWSS)¹. This entity is characterized by spike-and-wave complexes (SWC) that occurs most continuously (>85%) during slow or non-rapid-eye movement (NREM) sleep. The close relationship between CSWSS and Landau-Kleffner syndrome (LKS), as well as with the benign childhood epilepsy with centrotemporal spikes (BECTS), is suggested by several reports^2-12.

It is considered a rare syndrome, has received considerable attention in Europe and has a few reports from North America^13-22. In 1996, a large series of patients with epilepsy, observed by 14 epilepsy centers in the Lombardy region, between 1990 and 1994, was aimed at verifying the applicability of the ILAE classification, revised in 1989. They observed 10342 patients and only 5 were classified as CSWSS. In 1989, Morikawa et al. reported 31 cases out of 12854 patients observed during 10 years¹⁵. Since 1971, about 200 cases with generalized SWC and only seven with focal distribution on EEG have been reported^13,14. We studied 8 patients with focal CSWSS and 7 with generalized form, about their clinical and EEG features.

METHOD

We observed 26 patients with CSWSS at our electroencephalography (EEG) laboratory during the past three years, but only 15 could be studied about their clinical and EEG features. Most of them (13/ 15), disclosed partial simple seizures and only two with generalized seizures (none had family history of seizures). The age at diagnosis ranged from 4 to 13 year old (mean 8.6 years), with a follow-up period of 3 to 10 years. Overnight EEG was performed on 2 patients and conventional EEG was repeated every 1 to 6 months during the follow-up.

RESULTS

Table 1 summarizes the clinical profiles of the patients and the EEG findings. During the awake and light sleep states, the EEG was abnormal in most of the patients (9/ 11) with multifocal spikes. The background EEG activity (BA) was normal in 5 cases (5/12) and abnormal in 2 cases (2/12).

The most characteristic EEG changes occurred during sleep in all cases. Nine cases (60%) displayed nearly continuous left focal discharges (>85% of the NREM sleep time) while diffuse SWC with > 85% of NREM sleep was seen in 6 cases (40%).

The treatment was effective in improving the clinical seizures, but not the EEG pattern in all of them, with either phenobarbital, carbamazepine, clobazan and nitrazepan. The neuroradiological investigations (CT scan and MRI) were normal in 7 patients (7/ 12) and abnormal in 5 cases (5/ 12), showing periventricular leukomalacia, hydrocephalus, diffuse brain atrophy and arachnoid cysts.

The following case illustrates our study.

WNS, a 13 year-old boy was first seen at the age of 3 when he was referred with a history of partial motor seizures and non-progressive encephalopathy (neonatal hypoxic-ischemic brain damage). His development was abnormal with marked motor deficit. MRI showed periventricular leukomalacia with brain atrophy. At the age of 3 an awake and sleep EEG was carried out for about 30 minutes, displaying slow BA with rare spikes over the left frontal and parietal regions. Further EEGs, done at 4, 5 and 7 year-old disclosed multifocal discharges of spikes and SWC that markedly increased during NREM sleep, but without continuous spikes (<50%). At 8 year-old, after 4 months seizure-free, another EEG was performed for 60 minutes and showed nearly continuous generalized activity during NREM sleep. At age 9, an overnight EEG still showed the characteristic of CSWSS (Fig 1). In 1997, at 13 year-old and already seizure-free, another EEG was carried out disclosing only bilateral temporal discharges, without the CSWSS.

DISCUSSION

The CSWSS is primarily an EEG diagnosis and secondarily a clinical one. The main diagnostic criterion is the occurrence of SWC nearly continuously during the NREM sleep but not during the awake state or REM sleep and must involve at least 85% of NREM sleep¹. CSWSS occurs with a male to female ratio of 2:1. Onset appears to be age-related, occurring between the ages of 5 to 12 years^5,12,15,16. In our patients we first recorded the CSWSS between the ages of 4 and 13 (mean 6.2). Seven of them were male and the others were female.

The differential diagnosis of CSWSS includes BECTS, LKS and Lennox-Gastaut syndrome (LGS). In the first condition, there is an intense sleep activation of interictal abnormalities, however, it never reaches the 85% threshold required for the diagnosis of CSWSS^1,12. In LKS there is activation of paroxysmal abnormalities during sleep onset and during each REM period, a distinguishing feature of CSWSS¹². In LGS the SWC index is about 60% during the NREM sleep.

There is no specific association of neurological findings with CSWSS. Eight out of 18 patients reported by Tassinari et al. had "encephalopathy" before the onset of the CSWSS, like 10 of our 15 patients²¹. Specific etiologies have not been completely defined but include mainly birth asphyxia, like 7 of our 15 patients, as well as meningitis, encephalopathy of unknown origin, congenital cytomegalovirus infection and cryptogenic category^1,8,12,16.

With regard to neuroimage studies (CT and MRI) in 12 patients, we found normal features in 6 cases, periventricular leukomalacia with and without diffuse brain atrophy in 4 cases and hydrocephalus in 1 case.

Regarding EEG findings, in 6 of our 15 cases the distribution of the activity was generalized SWC discharges without any clinical manifestations during NREM sleep and were completely suppressed during REM sleep and wakefulness state. However, cases have been described with discharges relatively focal in distribution, like 9 of our 15 cases, or characterized by nearly continuous diffuse bisynchronous sharp waves and not SWC, a controversy that the literature has called generalized SWC^{1,11-14,16-18}. These features support the assumption that the pathophysiological background of CSWSS may be associated to the reticular system, giving rise to paroxysmal bilateral synchronous SW, suggesting that CSWSS pattern is of a focal, rather than a generalized nature¹.

The basic eletrophysiological mechanisms involved in CSWSS are not known and some questions are unanswered as the link to sleep activities, functional and structural consequences on the developing brain. According to some authors, the secondary bilateral synchrony (SBS) was suggested to be the pathophysiology of CSWSS, with statistical analysis of SW activity such as coherence and phase analysis in addition to the clinical-EEG study^1,15,19. In this case, the corpus callosum may play a role in the generation of the SBS in CSWSS¹⁹.

A study of electrophysiology of CSWSS in LKS, with EEG, intracarotid amobarbital and methohexital suppression tests, registered the SWC arising unilaterally, despite the apparent billaterality and widespread distribution, what was later correlated with electrocorticographic recording²¹.

There is no specific anti-epileptic treatment for this disorder because clinical seizures have not posed a management problem and have responded to a variety of drugs, like our 15 cases. On the other hand, the EEG abnormality is generally refractory. Few reports concerning treatment of CSWSS are found in the literature. Patry et al. reported nitrazepan to be effective in improving the EEG pattern but not the clinical manifestations¹⁷. Yasuhara et al. showed that clonazepan gradually improved the clinical features and EEG pattern in five patients²². Nitrazepan and clobazan have apparently abolished the characteristic SWC activity and improved neuropsychological function^3,4,8,18. In our opinion it may have been a coincidental remission.

There is a strong temporal correlation between the onset of CSWSS and the neupsychological deterioration in its nature, severity and prognosis. This probably depend on many factors, including the location of the main epileptic focus, the duration of the CSWSS and the state of maturation of the concerned brain areas at onset. All of our 15 cases had disorders such as short attention, hyperactive behavior, speech disturbance, spatial disorientation and intellectual deterioration. Besides the severe neuropsychological disorders, the partial seizures had the usual favorable prognosis.

We believe that this distressing disorder has been overlooked and that the routine EEG sleep studies on epileptic children may disclose additional cases of CSWSS.

Dr. Marcus A. S. Batista. - Rua Olavo Bilac 3381/502 - 64001-600 Teresina PI - Brasil.

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*

Discipline of Neurology, Federal University of São Paulo (UNIFESP)/ Paulista School of Medicine (EPM):

Childhood neurologist;

**

Neurologist;

***

Eletroencephalografist. Presented as abstract during the XXIIInd International Epilepsy Congress. Dublin, Ireland, 1998. Aceite: 20-abril-1999.

Publication Dates

• Publication in this collection
  06 Dec 2000
• Date of issue
  Sept 1999

History

• Accepted
  20 Apr 1999